In a conventional petroleum or petrochemical refinery process and system, crude feedstock is processed by a crude distillation unit. The crude feedstock may comprise crude oil and/or feedstock having undergone partial processing (“intermediate refinery feedstock”). The crude distillation unit produces a naphtha fraction, together with a number of other fractions useful in production of refined oil products, for example, gasoline, jet fuel, diesel, etc., and fractions useful for the production of specialty chemicals.
Naphtha is mainly a mixture of straight-chain, branched and cyclic aliphatic hydrocarbons. The naphtha fraction is primarily composed of paraffins, olefins, naphthenes and aromatics. Paraffins are alkane hydrocarbons of general formula CnH2n+2 which may be substituted, and wherein n is a whole number; e.g., from 1-14. The term “paraffins” is also generally understood to include isoparaffins. Olefins are hydrocarbons having at least one carbon-carbon double bond, such as an alkenes of general formula CnH2n which may be substituted and wherein n is a whole number; e.g., from 2-14. The olefin fraction ma also comprise alkynes of general formula CnH2n−2 which may be substituted and wherein n is a whole number—e.g., from 2-14. When n is greater than 12, the fraction may be referred to as distillates; e.g., jet fuel, diesel, etc. Higher n fractions may be usefill for other purposes. Olefins (including substituted olefins) where n=12-14 may be found in both the naphtha fraction and the distillates fraction. The naphthenes include cycloalkanes and alkyl substituted cycloalkanes. Many naphthenes are chemical precursors to the aromatics. The aromatics found in a petroleum or petrochemical feedstock include a range of conjugated hydrocarbon rings and alkyl substituted conjugated hydrocarbon rings.
The whole range naphtha fraction from the crude distillation unit is processed in a naphtha splitter producing an overhead stream (typically referred to as a Light Straight Run or LSR or simply light naphtha), and a bottoms stream of heavy naphtha. Naphtha is generally divided into light Naphtha having from five to nine carbon atoms per molecule and heavy naphtha having from seven to twelve carbons per molecule.
The light naphtha is rich in paraffins, and the heavy naphtha is rich in naphthenes and aromatics. Typically, light naphtha contains naphthenes, such as cyclohexane and methylcyclopentane, and linear and branched paraffins, such as hexane and pentane. Light naphtha typically contains 60% to 99% by weight of paraffins and cycloparaffins. Light naphtha can be characterized as a petroleum distillate having a molecular weight range between about 70 grams per mole (g/mol) and about 150 g/mol, a specific gravity range between about 0.6 grams per cubic centimeter (g/cm3) and about 0.9 g/cm3, a boiling point range between about 50° F. and about 320° F. and a vapor pressure between about 5 millimeter mercury (mm Hg) (torr) and about 500 mm Hg (torr) at room temperature. Light naphtha may be obtained from crude oil, natural gas condensate or other hydrocarbons streams by a variety of processes, e.g., distillation.
The heavy naphtha bottoms stream is hydrotreated to remove sulphur and other contaminants, obtaining a sweet naphtha, which is fed to a naphtha reformer where it may be combined with other intermediate sweet naphtha streams, for example, sweet natural gas condensates and hydrocracker naphtha. In the naphtha reformer, the naphtha components are reformulated into components of a gasoline product.
A naphtha reformer is usually a high severity reformer, which produces aromatics, including benzene, toluene and xylenes (“BTX”), as well as other aromatics that enable the reformate to have an octane quality sufficient to meet gasoline octane specifications. Benzene, toluene and xylenes may all also be used in the production of petrochemical derivatives. Of the xylenes that may be used in the production of petrochemical derivatives, para- and ortho-xylene are worth particular mention, although meta-xylenes may also be of value.
High severity reformers are run at high temperatures (e.g., inlet temperatures of about 900 degrees Fahrenheit-around 480 degrees Celsius—or greater) with commercially available catalyst, and have long residence times. The residence time is a factor of the number of reactors and the amount of catalyst involved. High severity reformers typically involve four or five reactors in series. Also, at each reactor, heating to the noted inlet temperature is required in order to produce the desired gasoline products. High severity reformers are associated with high operating costs and may result in a significant volume loss across reactors of high economic value gasoline components.
U.S. Pat. No. 2,914,460 discloses reforming of hydrocarbons and particularly to an improved method for the aromatization of light naphtha fractions to produce a highly aromatic high octane product. The document teaches catalysts containing 0.01 to 1.0 wt. percent platinum or 0.1 to 2.0 wt. percent palladium dispersed upon a highly pure alumina support such as is obtained from aluminum alcoholate or from an alumina hydrosol prepared by hydrolyzing aluminum metal with dilute acetic acid in the presence of very small catalytic amounts of mercury as suitable for hydroforming the light naphthas.
U.S. Pat. No. 3,003,948 discloses a process for decontamination of naphthas and the reforming of the decontaminated naphthas over a platinum group metal reforming catalyst and, more particularly to the decontamination over a first catalyst, dehydrogenation over a platinum-group metal catalyst, and aromatization of the dehydrogenated naphtha over the aforesaid first catalyst. In a preferred aspect, the document teaches a catalyst comprising oxides of chromium, molybdenum, and aluminum as the first catalyst.
U.S. Pat. No. 3,843,741 discloses a process of converting an aliphatic feedstock having an atmospheric boiling point of up to about 400° F. to aromatic hydrocarbons by contacting such feedstock with a ZSM-S type of zeolite at about 500° to 1500° F. and a space velocity of up to about 15 WHSV, Particularly, the document discloses use of a catalyst comprising a matrix of ZSM-5 type of crystalline zeolite and a second, inorganic component consisting essentially of at least about 80 weight percent silica. In a preferred aspect, the zeolite is Zn ZSM-5 or Zn Cu ZSM-5.
U.S. Pat. No. 5,037,529 discloses a dual stage reforming process comprising: (a) contacting a feed containing a straight chain paraffin containing 6 to 12 carbon atoms with a non-acidic catalyst, under dehydrocyclization conditions, where said catalyst comprises two components one of which two components is a non-acidic medium pore zeolite containing a modifier selected from the group consisting of tin, indium and thallium and a second of which two components is a reforming dehydrogenation/hydrogenation metal and producing an effluent (1) which has an aromatic content greater than that of the feed and (2) which comprises olefins produced under said dehdrocyclization conditions; (b) contacting the effluent with an acidic catalyst comprising a zeolite having a constraint index of 1 to 12, under conditions of temperature ranging from 400 atmospheric to 500 psig, a liquid hourly space velocity 0.1 to 10 and a hydrogen cofeed to effluent ratio of 0 to 10:1, to convert said olefins to gasoline to produce a reformate which has an aromatic content greater than that of the effluent or has an RON greater than that of the effluent or has both.
U.S. Pat. No. 5,200,375 discloses a process for regenerating a coked monofunctional catalyst composition resulting from catalysis in dehydrogenation and/or dehydrocyclization, wherein the coked monofunctional catalyst composition comprises a dehydrogenation/hydrogenation metal and a non-acidic microporous crystalline material wherein the dehydrogenation/hydrogenation metal is present in an amount which ranges from 0.1 to 20 weight percent; wherein said material contains 0.1 to 20 weight percent of tin, indium, thallium or lead; wherein the microporous crystalline material has an X-ray diffraction pattern of a zeolite which is selected from the group consisting of ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-48 and ZSM-50.
U.S. Pat. No. 5,658,453 discloses a process for selectively upgrading a naphtha feedstock comprising the steps of: (a) contacting the feedstock with an aromatization catalyst in an aromatization zone in the presence of hydrogen at aromatization conditions including a pressure of from atmospheric to below 10 atmospheres, a temperature of from 260 space velocity of from about 0.5 to 40 hr.sup.-1 to obtain an aromatization effluent stream; (b) separating the aromatization effluent stream to obtain a hydrogen-rich gas and an aromatics-rich intermediate stream containing a small proportion of olefins and dissolved hydrogen-containing gas; (c) contacting the aromatics-rich intermediate stream and a portion of the hydrogen-rich gas to provide a molar ratio of hydrogen to the intermediate stream of from about 0.005 to 0.08 in a selective saturation zone with a saturation catalyst comprising a platinum-group metal component and a refractory inorganic oxide at saturation conditions including a pressure of from about 100 kPa to 10 MPa, a temperature of from about 30 300 hr.sup.-1 to saturate at least about 70% of the contained olefins and less than about 1% of the aromatics and obtain a saturated effluent containing trace residual hydrogen-containing gas; and, (d) stabilizing the saturated effluent in a fractionator to remove trace residual hydrogen-containing gas and to obtain a stabilized aromatics-rich product.
U.S. Pat. No. 6,063,724 discloses a catalyst which effectuates the aromatization, reformation, and dehydrogenation of aliphatic, cycloaliphatic, and mixtures of aliphatic and cycloaliphatic hydrocarbons. The catalyst comprises an L-zeolite associated with a Group VIII metal such as platinum and having a rare earth metal ion incorporated therein. Particularly, the document discloses a catalytic material prepared by the process comprising the steps of: providing an L-zeolite; calcining the L-zeolite so as to substantially remove water, thereby providing a substantially anhydrous L-zeolite; incorporating the substantially anhydrous L-zeolite with at least one rare earth ion, thereby providing a rare earth ion incorporated L-zeolite; calcining the rare earth ion incorporated L-zeolite, thereby providing a calcined rare earth ion incorporated L-zeolite; and associating a Group VIII metal with the calcined rare earth modified L-zeolite thereby providing a catalytic material.
U.S. Pat. No. 6,190,534 discloses a process fir selectively upgrading a naphtha feedstock to obtain an aromatics-rich product having an increased octane number comprising the steps of: (a) contacting the naphtha feedstock in an olefin-forming zone with a nonacidic, non-zeolitic olefin-forming catalyst, comprising at least one platinum-group metal component and a nonacidic support, at olefin-forming conditions comprising a temperature of from about 350 to 650° C., pressure of from about 100 kPa to 4 MPa and liquid hourly space velocity of from about 0.1 to 100 hr−1 to dehydrogenate paraffins without substantial dehydrocyclization and produce an olefin-containing intermediate stream; and, (h) converting the olefin-containing intermediate stream to yield aromatics in an aromatization zone maintained at aromatization conditions comprising a temperature of from about 260 to 560° C., pressure of from about 100 kPa to 4 MPa and liquid hourly space velocity of from about 0.5 to 40 hr−1 in the presence of free hydrogen with a solid acid aromatization catalyst comprising a supported platinum-group metal component and recovering the aromatics-rich product.
U.S. Pat. No. 6,245,724 discloses reforming naphtha-containing hydrocarbon feedstreams wherein a naphtha stream containing at least about 25 wt % of C5 to C9 aliphatic and cycloaliphatic hydrocarbons is contacted with a modified reforming catalyst, e.g. ZSM-5, containing a dehydrogenation metal, e.g. zinc, which has been modified by contact with Group IIA alkaline earth metal, e.g. barium, or with an organosilicon compound in an amount sufficient to neutralize at least a portion of the surface acidic sites present on the catalyst. The resulting reformats contains a reduced content of C1 to C4 gas and a C8 aromatic fraction having an enhanced content of para-xyelene.
U.S. Pat. No. 8,362,310 discloses a hydrocarbon aromatization process comprising: adding a nitrogenate to a hydrocarbon stream to produce an enhanced hydrocarbon stream, wherein the hydrocarbon stream is substantially free of sulfur and wherein the nitrogenate comprises ammonia or one or more ammonia precursors that form ammonia in the reaction zone; contacting the enhanced hydrocarbon stream with an aromatization catalyst in a reaction zone, wherein the aromatization catalyst comprises a non-acidic L-zeolite support, platinum, and one or more halides; and recovering an effluent comprising aromatic hydrocarbons.
U.S. Pat. No. 8,419,929 discloses a naphtha productive aromatic hydrocarbon reforming system, which comprises a heating device and a reaction device connected with the heating device and is Characterized in that the bottom part of the reaction device is connected with a high-pressure separator, the high-pressure separator is connected with a stabilizer system and also connected with a feedstock supply system and a compressor; the lower part of the stabilizer system is connected with an extraction system, which is adapted to extract a mixed aromatic hydrocarbon from a stabilized hydrocarbon to form a raffinate oil stream and a mixed hydrocarbon stream, the extraction system is connected with a raffinate oil cutting system, which is adapted to separate the raffinate oil stream into 3 cuts, and, a light raffinate oil is recovered by the upper part of the raffinate oil cutting system, the middle part of the raffinate oil cutting system is connected with another reaction device (a reaction device) and the heating device, and coal oil is directly recovered by the lower part of the raffinate oil cutting system; and the other end of another reaction device is connected with a cooling device and the high-pressure separator. The document suggests use of platinum/rhenium catalysts in the aforesaid process.
U.S. Pat. No. 8,471,083 discloses a process for producing para-xylene comprising the steps of: (a) contacting a hydrocarbonaceous feed wherein at least 50 wt. % of said feed boils above 550° C., in a first reaction zone comprising a hydrocracking catalyst under hydrocracking conditions to form an effluent; (b) separating the effluent into at least a C8 containing fraction comprising at least 10 wt. % C8 paraffinic hydrocarbons; (c) providing the C8 containing fraction to a second reaction zone; (d) contacting the C8 containing fraction under reforming reaction conditions with a reforming catalyst comprising a medium pore zeolite having a silica to alumina molar ratio of at least 200, a crystallite size of less than 10 microns and an alkali content of less than 5000 ppm in a second reaction zone to produce a product stream comprising para-xylene and meta-xylene wherein the para-xylene to meta-xylene ratio is at least 0.9; and (e) separating the para-xylene from the product stream. Particularly, the document states that the use of a low acidity medium pore zeolite catalyst with a silica to alumina ratio of at least about 40 to 1, increases the yield of para-xylene from a given C8 paraffinic feedstock.
U.S. Patent Publication No. 2013/0261363 discloses a catalyst for catalytic reforming of naphtha, comprising: a) a noble metal comprising one or more of platinum, palladium, rhodium, ruthenium, osmium, and iridium; b) one or more alkali metals or one or more alkaline-earth metals from Groups 1 or 2 of the Periodic Table; c) a lanthanide-series metal comprising one or more elements of atomic numbers 57-71 of the Periodic Table; and d) a support; wherein an average bulk density of the catalyst is about 0.300 to about 1.00 gram per cubic centimeter, a noble metal content less than about 0.6 wt %, an alkali metal content of about 50 to about 1000 wppm, or an alkaline earth metal content of about 250 to about 5000 wppm, and a lanthanide-series metal content of about 0.05 to about 2 wt %.
Given the aforesaid state of the art, it can be said that there is a constant need to provide improved catalysts. More particularly, there is a need to provide catalysts which can improve the yield of aromatic compounds during the processing of light naphtha and especially, increase the yield of toluene. Additionally, there is a need to increase in the yield of dry gas, a quantum of C3 fraction.